Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/702/
690 
CIRRHOPODA. 
the mantle. Professor Burmeister describes 
the gills of Coronula diadema as broad mem¬ 
branous expansions, of a semicircular form, 
attached to the sides of the visceral mass by a 
narrow pedicle. They are composed of two 
tunics arranged in deep and narrow transverse 
plaits. The number of the branchiae in the 
Lepads varies from four to sixteen. They are 
composed of soft cellular tissue, and have a 
smooth surface. 
The arms (h, h, fig. 340), which constitute 
so large a portion of the general mass of all the 
Cirripeds, and which form their most distinc¬ 
tive feature, must be regarded as subservient 
chiefly to the function of respiration; although, 
by producing currents in the water, which 
bring food within reach of the jaws, they minis¬ 
ter also to the digestive function. In all the 
known species, both of Lepads and Balanids, 
these arms are twelve in number, six on either 
side, arranged symmetrically. Each arm is 
composed of a short fleshy peduncle, having 
three articulations, and two horny articulated 
processes, compressed laterally, of equal length, 
ciliated on their internal surfaces, and coiled 
up in a spiral of one turn. On their internal 
surface there is a coating of a black pigment in 
spots. Each joint is provided with a double 
row of hairs of different lengths. (Fig. 343.) 
Fig. 343. 
A part of one of the arms considerably magnified. 
In Anatifa, the first pair of arms is thicker and 
stronger than the others ; the sixth pair is the 
longest. Dr. Grant says, “ the arms are not 
only minutely jointed to their extreme points, 
but, also, the innumerable fine cilia which pro¬ 
ject inwards from their surface are themselves 
minutely jointed, and by the aid of the micro¬ 
scope, we can perceive that these jointed cilia 
are also ciliated on their margins.” 
When the animal is at rest, with the valves 
of the shell closed, the arms are coiled up, and 
lie close to one another; but, at other times, 
circumstances being favourable to the perform¬ 
ance of the function of respiration, they are ex¬ 
tended simultaneously so as to project from the 
shell,—radiate and plumose in their arrange¬ 
ment. Many species extend and contract their 
arms with considerable rapidity, as often as 
forty or sixty times in a minute ; the smaller 
species more frequently than the larger. 
Considering how extensive the surface is 
which is exposed in the arms between the two 
rows of cilia, and that a vessel seems to run 
immediately beneath the delicate covering of 
these organs in that situation, it appears proba¬ 
ble that the arms are very efficient agents in the 
function of respiration. 
Secretion.— We have failed to ascertain satis¬ 
factorily the structure of the secreting apparatus 
by which the shells of the Cirripeds are formed. 
In the Lepads, the organs must be imbedded 
in the ligamentous membrane by which the 
valves are united : and in the Balanids, they are 
arranged in six rows along the outer surface of 
the mantle, and around the base; but, as in 
acephalous mollusca, they are too small to ad¬ 
mit of their structure being particularly exa¬ 
mined. The external surface of the mantle in 
the Balanids has also the power of secreting 
calcareous matter, with which to increase the 
thickness of the shell. 
Reproduction.—It is not yet accurately de¬ 
termined what are the organs of reproduction 
in these animals. That which was regarded by 
Cuvier as the ovary in the Lepads, is supposed 
by Professor Wagner and M. St. Ange to be 
the testicle; while Professor Burmeister has 
satisfied himself that it is the liver. The ex¬ 
tent, structure, and relations of the ovary are 
still doubtful. It is certain, however, that all 
the known Cirripeds are hermaphrodite. 
The testicle, according to Professor Wagner 
and M. St. Ange, is a large granular organ 
(1h fië- 344), expanded over the sides of the 
Fig. 344. 
visceral mass, and around the digestive canal, 
from the stomach to the anus, passing even into 
the bases of the arms, immediately beneath the 
muscular tunics which cover the body on both 
sides. It is composed of numerous minute 
lobules, about 3^th of an inch in diameter in 
the common Lepads, soft, white, grouped toge¬ 
ther by branched ducts (q, q, fig. 344), which, 
after uniting into three or four principal trunks,* 
meet in a large central receptacle (r), some¬ 
what analogous in relative function to the vas 
deferens of vertebrate animals. The seminal 
fluid passes from this central, receptacle by a 
short and straight duct into a large canal (t, t), 
which may be compared to the seminal vesicle. 
It pursues a tortuous course towards the base 
of the tubular process, where (k) it is joined by 
its fellow of the other side, and enters the canal 
* This description does not accord with the result 
of Pro lessor Burmeister’s researches. Instead of 
a regular series of branched vessels, he says that 
he met with nothing but an irregularly arranged 
mesh of thready fibres lying between what he be¬ 
lieved to be the liver (described above as the testi¬ 
cle) and the intestinal canal.
        

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